The present invention relates to magnetic recording media, such as thin film magnetic recording disks. The present invention has particular applicability to high areal density longitudinal magnetic recording media exhibiting low noise and enhanced magnetic performance.
Magnetic recording media are extensively employed in the computer industry and can be locally magnetized by a write transducer or write head to record and store information. The write transducer creates a highly concentrated magnetic field which alternates direction based upon bits of the information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium, grains of the recording medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The magnetization of the recording medium can subsequently produce an electrical response to a read sensor, allowing the stored information to be read.
There is an ever increasing demand for magnetic recording media with higher storage capacity and lower noise. Efforts, therefore, have been made to reduce the space required to magnetically record bits of information while maintaining the integrity of the information. The space necessary to record information in magnetic recording media depends upon the size of transitions between oppositely magnetized areas. It is, therefore, desirable to produce magnetic recording media that will support the smallest transition size possible. However, the signal output from the transition must avoid excessive noise to reliably maintain the integrity of the stored information. Media noise is generally characterized as the sharpness of a signal on readback against the sharpness of a signal on writing and is generally expressed as signal-to-noise ratio (SNR) of the medium.
The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of coercivity (Hc), magnetic saturation (Ms), magnetic remanance (Mr), coercivity squareness (S*), SNR, and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements.
The linear recording density can be increased by increasing the Hc of the magnetic recording medium, and can be accomplished by decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise in thin films is a dominant factor restricting increased recording density of high density magnetic hard disk drives, and is attributed primarily to inhomogeneous and large grain size and intergranular exchange coupling. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
Longitudinal magnetic recording media containing cobalt (Co) or Co-based alloy magnetic films with a chromium (Cr) or Cr alloy underlayer deposited on a non-magnetic substrate have become the industry standard. For thin film longitudinal magnetic recording media, the desired crystallized structure of the Co and Co alloys is hexagonal close packed (HCP) with uniaxial crystalline anisotropy and a magnetization easy direction along the c-axis is in the plane of the film. The better the in-plane c-axis crystallographic texture, the more suitable is the Co alloy thin film for use in longitudinal recording to achieve high remanance. For very small grain sizes coercivity increases with increased grain size. The large grains, however, result in greater noise. Accordingly, there is a need to achieve high coercivities without the increase in noise associated with large grains. In order to achieve low noise magnetic recording media, the Co alloy thin film should have uniform small grains with grain boundaries capable of magnetically isolating neighboring grains. This type of microstructural and crystallographic control is typically attempted by manipulating the deposition process, grooving the substrate surface and proper use of an underlayer.
If the uniformity of the grains in the underlayer structure is improved, this uniformity propagates to the uniformity of the grains in the magnetic layer or layers, thereby achieving high. SNR. However, such uniformity must be effected without disturbing the crystallographic orientation of the magnetic grains. This objective is not easily achieved.
There exists a continuing need for high areal density longitudinal magnetic recording media exhibiting high coercivity and high SNR.
An advantage of the present invention is a magnetic recording medium for high areal recording density exhibiting low noise and high coercivity, with a magnetic layer or layers exhibiting a highly uniform grain size.
Additional advantages and features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a magnetic recording medium comprising: a chromium-molybdenum-tantalum (CrMoTa) underlayer; and a magnetic layer over the underlayer, the magnetic layer having a uniform grain size with a standard deviation less than 0.4.
Embodiments of the present invention comprise a composite underlayer system containing a first Cr layer, e.g., elemental chromium, and a Cr100-x-yMoxTay layer thereon, wherein x is 1 to 12, e.g., 8 to 12, and y is 1 to 6, e.g., 2 to 4. Embodiments of the present invention further include magnetic recording media comprising a non-magnetic substrate, a seedlayer on the substrate, a Cr underlayer on the seedlayer, a CrMoTa underlayer on the Cr underlayer, an interlayer on the CrMoTa underlayer and a magnetic layer on the interlayer. Embodiments of the present invention further include anti-ferromagnetically coupled ferromagnetic films with a spacer layer, with or without an interface layer on one or both sides of the spacer layer positioned between the ferromagnetic layers.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.